U.S. patent number 10,113,155 [Application Number 14/402,165] was granted by the patent office on 2018-10-30 for steviol glycosyltransferase and gene encoding same.
This patent grant is currently assigned to SUNTORY HOLDINGS LIMITED. The grantee listed for this patent is SUNTORY HOLDINGS LIMITED. Invention is credited to Eiichiro Ono.
United States Patent |
10,113,155 |
Ono |
October 30, 2018 |
Steviol glycosyltransferase and gene encoding same
Abstract
The present invention provides steviol glycosyltransferase and a
method for producing a steviol glycoside using this enzyme. The
present invention provides a transformant transformed with a gene
for steviol glycosyltransferase and a method for preparing such a
transformant.
Inventors: |
Ono; Eiichiro (Osaka,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SUNTORY HOLDINGS LIMITED |
Osaka |
N/A |
JP |
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Assignee: |
SUNTORY HOLDINGS LIMITED
(Osaka, JP)
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Family
ID: |
49673485 |
Appl.
No.: |
14/402,165 |
Filed: |
May 29, 2013 |
PCT
Filed: |
May 29, 2013 |
PCT No.: |
PCT/JP2013/065518 |
371(c)(1),(2),(4) Date: |
November 19, 2014 |
PCT
Pub. No.: |
WO2013/180306 |
PCT
Pub. Date: |
December 05, 2013 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150218533 A1 |
Aug 6, 2015 |
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Foreign Application Priority Data
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May 30, 2012 [JP] |
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2012-123349 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C12P
15/00 (20130101); C12Y 204/01 (20130101); C12N
9/1051 (20130101); C12N 15/8245 (20130101); C12P
19/56 (20130101) |
Current International
Class: |
C12N
9/10 (20060101); C12P 19/44 (20060101); C12N
15/82 (20060101); C12P 19/56 (20060101); C12P
15/00 (20060101); C07K 14/415 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1 897 951 |
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Dec 2010 |
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EP |
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54-030199 |
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Mar 1979 |
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JP |
|
62-155096 |
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Jul 1987 |
|
JP |
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5-255372 |
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Oct 1993 |
|
JP |
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2011-512801 |
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Apr 2011 |
|
JP |
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2008/034648 |
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Mar 2008 |
|
WO |
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2012/075030 |
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Jun 2012 |
|
WO |
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2013/176738 |
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Nov 2013 |
|
WO |
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Other References
Richman, Alex, et al. "Functional genomics uncovers three
glucosyltransferases involved in the synthesis of the major sweet
glucosides of Stevia rebaudiana." The Plant Journal 41.1 (2005):
56-67. cited by examiner .
Noguchi, Akio, et al. "Local differentiation of sugar donor
specificity of flavonoid glycosyltransferase in Lamiales." The
Plant Cell 21.5 (2009): 1556-1572. cited by examiner .
Kinghorn, A. Douglas, ed. Stevia: the genus Stevia. CRC Press, 2003
(Year: 2003). cited by examiner .
Richman, Alex, et al. "Functional genomics uncovers three
glucosyltransferases involved in the synthesis of the major sweet
glucosides of Stevia rebaudiana." The Plant Journal41.1 (2005):
56-67. (Year: 2005). cited by examiner .
Shibata et al., "Steviol and steviol-glycoside: glycosyltransferase
activities in Stevia rebaudiana Betoni--purification and partial
characterization", Arch. Biochem. Biophys., vol. 321, No. 2, pp.
390-396 (1995). cited by applicant .
Brandle et al., "Steviol glycoside biosynthesis", Phytochemistry,
vol. 68, No. 14, pp. 1855-1863 (2007). cited by applicant .
Richman et al., "Functional genomics uncovers three
glucosyltransferases involved in the synthesis of the major sweet
glucosides of Stevia rebaudiana ", Plant J., vol. 41, No. 1 , 2005,
pp. 56-67 (2005). cited by applicant .
Kasai et al., "Stevia-ha no Kanmi Diterpene
Haitotai-Rebaudioside-A, -D, -E Oyobi Kanren Haitotai no Gosei
Narabini Kanmi to Kagaku Kozo tono Sokan-", Journal of the Chemical
Society of Japan, No. 5, pp. 726-735 (1981), including English
language Abstract. cited by applicant .
Mizutani et al., "Diversification of P450 genes during land plant
evolution ", Annu. Rev. Plant Biol., vol. 61, pp. 291-315 (2010).
cited by applicant .
Ono et al., "Diterpene Kanmiryo Rebaudioside A no Seigosei ni
Kakawaru Stevia Shinki Haitotaika Koso no Dotei", Dai 54 Kai
Proceedings of the Annual Meeting of the Japanese Society of Plant
Physiologists, 3aH10 (464), Mar. 14, 2013, p. 230. cited by
applicant .
U.S. Appl. No. 14/386,934 to Eiichiro Ono, filed Sep. 22, 2014.
cited by applicant .
U.S. Appl. No. 14/383,698 to Eiichiro Ono et al., filed Sep. 8,
2014. cited by applicant .
International Search Report for PCT/JP2013/065518, dated Jul. 9,
2013. cited by applicant .
Tanaka, "Improvement of taste of natural sweeteners", Pure &
Appl. Chem., vol. 69, No. 4, pp. 675-683 (1997). cited by applicant
.
Extended European Search Report issued in EP Patent Application No.
13797812.8, dated Oct. 28, 2015. cited by applicant .
Osmani et al., "Substrate specificity of plant UDP-dependent
glycosyltransferases predicted from crystal structures and homology
modeling," Phytochemistry, vol. 70, pp. 325-347, 2009. cited by
applicant .
Orihara et al., "Biotransformation of Steviol by Cultured Cells of
Eucalyptus perriniana and Coffea arabica" Phytochemistry, vol. 30,
No. 12, pp. 3989-3992 (1991). cited by applicant .
Humphrey et al., "Spatial organisation of four enzymes from Stevia
rebaudiana that are involved in steviol glycoside synthesis" Plant
Mol. Biol., vol. 61, pp. 47-62 (2006). cited by applicant.
|
Primary Examiner: Visone; Lee A
Assistant Examiner: Fan; Weihua
Attorney, Agent or Firm: Greenblum & Bernstein,
P.L.C.
Claims
The invention claimed is:
1. A polynucleotide selected from: a polynucleotide comprising the
nucleotide sequence of SEQ ID NO: 1; and a polynucleotide
comprising a heterologous regulatory element operably linked to a
polynucleotide sequence encoding a protein consisting of the amino
acid sequence of SEQ ID NO: 2.
2. A non-human transformant comprising the polynucleotide of claim
1.
3. The non-human transformant according to claim 2, which is a
plant.
4. A method comprising culturing or cultivating the non-human
transformant according to claim 2 to produce the protein consisting
of the amino acid sequence of SEQ ID NO: 2.
5. The method of claim 4, further comprising: producing a steviol
glycoside by contacting the protein consisting of the amino acid
sequence of SEQ ID NO: 2 produced by the non-human transformant
with a UDP-sugar and a compound represented by formula (I):
##STR00017## where: R.sub.1 represents H, a glucose monomer, or a
glucose dimer, and R.sub.2 represents H or a glucose monomer.
6. A method for producing a steviol glycoside, comprising:
contacting, outside of a stevia plant, a protein consisting of the
amino acid sequence of SEQ ID NO: 2 with a UDP-sugar and a compound
represented by formula (I): ##STR00018## where: R.sub.1 represents
H, a glucose monomer, or a glucose dimer, and R.sub.2 represents H
or a glucose monomer.
7. The method according to claim 6, wherein the sugar in the
UDP-sugar is a hexose.
8. The method according to claim 6, wherein the sugar in the
UDP-sugar is selected from the group consisting of glucose,
mannose, and galactose.
9. The method according to claim 6, wherein the compound is
steviol, steviolmonoside, steviolbioside, rubusoside, or Compound
Y: ##STR00019##
10. The method according to claim 6, wherein the sugar in the
UDP-sugar is glucose.
11. The method according to claim 6, wherein the steviol glycoside
is steviolmonoside, steviolbioside, stevioside, rubusoside,
Compound X: ##STR00020## or any combination thereof.
12. The non-human transformant according to claim 2, wherein the
polynucleotide is inserted into an expression vector.
13. A method for producing an extract of the non-human transformant
according to claim 2 or of a culture of the non-human transformant
according to claim 2, the method comprising: providing the
transformant according to claim 2 or the culture of the
transformant, and obtaining an extract of the transformant or of
the culture of the transformant.
14. A method for producing a food, a pharmaceutical preparation, or
an industrial raw material, the method comprising: providing an
extract of the transformant according to claim 2 or of a culture of
the transformant, adding the extract to a raw material of a food, a
pharmaceutical preparation, or an industrial raw material, and
preparing the food, the pharmaceutical preparation, or the
industrial raw material.
15. The method according to claim 14, wherein the food is selected
from fermented foods, fruit drinks, soft drinks, sports drinks,
tea, bakery products, noodles, pastas, cooked rice, sweets, bean
curd, ham, bacon, sausage, fish cake (kamaboko), deep-fried fish
cake (ageten), and puffy fish cake (hanpen).
16. The method according to claim 15, wherein the fermented foods
include alcoholic beverages, tea, medicinal liquor, sweet cooking
sherry (mirin), vinegar, soy sauce, miso (bean paste), and
yogurt.
17. The method according to claim 14, wherein the pharmaceutical
preparation is selected from cream, gel, lipstick, facial pack,
ointment, dentifrice, and cleansing foam.
Description
SEQUENCE LISTING
The instant application contains a Sequence Listing which has been
submitted electronically in ASCII format and is hereby incorporated
by reference in its entirety. Said ASCII copy, created on Mar. 10,
2015, is named P46497_SL.txt and is 12,286 bytes in size.
TECHNICAL FIELD
The present invention relates to a protein having steviol glycoside
synthesis activity and a polynucleotide encoding the same, a method
for producing a steviol glycoside by means of this protein, a
transformant that highly expresses steviol glycosyltransferase, as
well as a steviol glycoside produced by the above method and use
thereof.
BACKGROUND ART
Leaves of stevia belonging to the family Asteraceae (Stevia
rebaudiana) contain a secondary metabolite called steviol, a kind
of diterpenoid, and steviol glycosides are used as calorie-less
sweeteners in food industries because they are about 300 times
sweeter than table sugar. Obesity has grown internationally as a
serious social issue, and the demand for calorie-less sweeteners
has been increasing day by day also in terms of health promotion
and medical expense reduction. Although aspartame, an artificially
synthesized amino acid derivative, and acesulfame potassium are now
used as artificial sweeteners, naturally occurring calorie-less
sweeteners like steviol glycosides are expected to be safer and
more likely to gain public acceptance.
As a result of sugar modification, stevia glycoside is finally
converted into a glycoside with four sugar molecules, which is
called rebaudioside A (FIG. 1). Stevioside, a trisaccharide
glycoside of steviol serving as a precursor of rebaudioside A, is
the highest in quantity; and hence rebaudioside A and stevioside
are main substances responsible for the sweetness of stevia. In
addition to these, other glycosides which appear to be reaction
intermediates and analogues with different types of sugars are
known to be present.
The enzyme gene leading to biosynthesis of rebaudioside A has been
isolated through expressed sequence tag (EST) analysis of stevia
(Non-patent Documents 1 and 2, Patent Document 1). Steviol is
generated when ent-kaurenoic acid, which is a precursor of the
diterpenoid gibberellin serving as a plant hormone, is hydroxylated
at the 13-position by the action of ent-kaurenoic acid
13-hydroxylase (EK13H), which is a cytochrome P450 enzyme (FIG. 2)
(Non-patent Document 3, Patent Document 1). Steviol is first
glycosylated (monoglucosylated) at the 13-position hydroxy group by
the action of UGT85C2 to thereby generate steviolmonoside.
Steviolmonoside is further glucosylated at the 2-position of the
13-position glucose to thereby generate a disaccharide glucoside of
steviol, called steviolbioside, or is further glucosylated at the
19-position carboxyl group to thereby generate a diglucoside of
steviol, called rubusoside. When the thus generated steviolbioside
and rubusoside are further glucosylated, steviol glycosides
including stevioside and rebaudioside A would be generated. Enzyme
genes known to be involved in the generation of steviol glucosides
are UGT74G1 and UGT76G1.
UGT74G1 is known to catalyze glucosylation at the 19-position of
steviolmonoside (Non-patent Document 1). UGT74G1 also causes
glucosylation of steviolbioside to thereby generate stevioside, a
triglucoside of steviol. This stevioside is the highest in content
in stevia leaves and is known to be about 250 to 300 times sweeter
that table sugar. This stevioside is further glucosylated by the
action of UGT76G1 to generate rebaudioside A, a tetraglucoside of
steviol, which is considered to be the sweetest (350 to 450 times
sweeter than table sugar) and to have a good quality of taste.
Steviol glycosides are reported to improve their quality of taste
and sweetness levels, particularly upon addition of a branched
sugar to glucose at the 13-position (Non-patent Document 4, Patent
Document 2). Thus, glycosyltransferases catalyzing these reactions
would be important enzymes responsible for determining the
sweetness properties of stevia.
Previous studies (Non-patent Document 2) have reported several
types of glycosyltransferases (UGTs) as a result of EST analysis on
stevia leaves, but detailed enzyme activity has not been fully
examined for all of these enzymes.
PRIOR ART DOCUMENTS
Patent Documents
Patent Document 1: EP 1 897 951 B1 Patent Document 2: JP 5-255372
A
Non-Patent Documents
Non-patent Document 1: Brandle and Telmer (2007) Phytochemistry 68,
1855-1863 Non-patent Document 2: Richman et al (2005) Plant J. 41,
56-67 Non-patent Document 3: Mizutani and Ohta (2010) Annu. Rev.
Plant Biol. 61, 291-315 Non-patent Document 4: Kasai et al (1981)
Journal of the Chemical Society of Japan 5, 726-735
SUMMARY OF THE INVENTION
Problem to be Solved by the Invention
As a result of extensive and intensive efforts, the inventors of
the present invention have succeeded in identifying an enzyme
catalyzing sugar addition reaction to glucose at the 13-position of
a steviol glycoside in stevia, as well as a gene sequence encoding
this enzyme. The present invention is based on the above
finding.
Means to Solve the Problem
Namely, the present invention is as follows.
[1] A protein of any one selected from the group consisting of (a)
to (c) shown below:
(a) a protein which consists of the amino acid sequence shown in
SEQ ID NO: 2;
(b) a protein which consists of an amino acid sequence with
deletion, substitution, insertion and/or addition of 1 to 7 amino
acids in the amino acid sequence shown in SEQ ID NO: 2 and which
has the activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by the following formula (I); and (c) a protein which
has an amino acid sequence sharing a sequence identity of 99% or
more with the amino acid sequence shown in SEQ ID NO: 2 and which
has the activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by the following formula (I)
##STR00001## (wherein R.sub.1 represents H, a glucose monomer or a
glucose dimer, and R.sub.2 represents H or a glucose monomer). [2]
The protein according to [1] above, wherein the sugar molecule is a
hexose. [3] The protein according to [1] above, wherein the sugar
molecule is selected from the group consisting of glucose, mannose
and galactose. [4] The protein according to [1] above, wherein the
compound is steviol, steviolmonoside, steviolbioside, rubusoside or
Compound Y
##STR00002## [5] A polynucleotide selected from the group
consisting of (a) to (d) shown below: (a) a polynucleotide
containing the nucleotide sequence shown in SEQ ID NO: 1; (b) a
polynucleotide encoding a protein which consists of the amino acid
sequence shown in SEQ ID NO: 2; (c) a polynucleotide encoding a
protein which consists of an amino acid sequence with deletion,
substitution, insertion and/or addition of 1 to 7 amino acids in
the amino acid sequence shown in SEQ ID NO: 2 and which has the
activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by the following formula (I); and (d) a polynucleotide
encoding a protein which has an amino acid sequence sharing a
sequence identity of 99% or more with the amino acid sequence shown
in SEQ ID NO: 2 and which has the activity to add a sugar
molecule(s) to --OR.sub.1 at the 13-position and --COOR.sub.2 at
the 19-position of a compound represented by the following formula
(I)
##STR00003## (wherein R.sub.1 represents H, a glucose monomer or a
glucose dimer, and R.sub.2 represents H or a glucose monomer). [6]
The polynucleotide according to [5] above, wherein the sugar
molecule is a hexose. [7] The polynucleotide according to [5]
above, wherein the sugar molecule is selected from the group
consisting of glucose, mannose and galactose. [8] The
polynucleotide according to [5] above, wherein the compound is
steviol, steviolmonoside, steviolbioside, rubusoside or Compound
Y
##STR00004## [9] A non-human transformant transformed with the
polynucleotide according to [5] above. [10] The transformant
according to [9] above, wherein the polynucleotide is inserted into
an expression vector. [11] The transformant according to [9] above,
which is a plant. [12] An extract of the transformant according to
[9] above. [13] A food, a pharmaceutical preparation or an
industrial raw material, which comprises the extract according to
[12] above. [14] A method for producing a protein, which comprises
culturing the non-human transformant according to [9] above,
wherein the protein has the activity to add a sugar molecule(s) to
--OR.sub.1 at the 13-position and --COOR.sub.2 at the 19-position
of a compound represented by the following formula (I)
##STR00005## (wherein R.sub.1 represents H, a glucose monomer or a
glucose dimer, and R.sub.2 represents H or a glucose monomer). [15]
A method for producing a steviol glycoside, which comprises using
the non-human transformant according to [9] above. [16] The method
according to [15] above, wherein the steviol glycoside is
steviolmonoside, steviolbioside, stevioside, rubusoside,
##STR00006## or any combination thereof. [17] A method for
producing a steviol glycoside, which comprises the step of reacting
the protein according to [1] above, a UDP-sugar and a compound
represented by the following formula (I)
##STR00007## (wherein R.sub.1 represents H, a glucose monomer or a
glucose dimer, and R.sub.2 represents H or a glucose monomer). [18]
The method according to [17] above, wherein the sugar in the
UDP-sugar is glucose. [19] The method according to [17] above,
wherein the steviol glycoside is steviolmonoside, steviolbioside,
stevioside, rubusoside,
##STR00008## or any combination thereof.
Effects of the Invention
The protein of the present invention and a polynucleotide encoding
the same can be used for efficient production of steviol glycosides
(e.g., steviolmonoside, steviolbioside, stevioside, rubusoside,
Compound X, Compound Y, Compound Z). Moreover, the transformants of
the present invention are rich in steviol glycosides (e.g.,
steviolmonoside, steviolbioside, stevioside, rubusoside, Compound
X, Compound Y, Compound Z), and hence steviol glycosides (e.g.,
steviolmonoside, steviolbioside, stevioside, rubusoside, Compound
X, Compound Y, Compound Z) can be efficiently extracted and
purified from these transformants.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows the names and structures of steviol glycoside members.
In FIG. 1, "Glc" denotes glucose. Likewise,
"Glc-Glc(.beta.2.fwdarw.1)" denotes that "Glc-Glc" are linked to
each other via a .beta.2,1 glycosidic linkage, while
"Glc-Glc(.beta.3.fwdarw.1)" denotes that "Glc-Glc" are linked to
each other via a .beta.3,1 glycosidic linkage.
FIG. 2 shows putative biosynthetic pathways of steviol
glycosides.
FIG. 3 shows the SDS-PAGE results obtained for UGT73E1 homologous
protein 1 expressed in E. coli. Panel A shows a CBB-stained image
obtained for the pellet fraction, while panel B shows a CBB-stained
image obtained for the fraction eluted with an imidazole solution.
The asterisks each represent an expressed recombinant protein.
FIG. 4 shows the enzyme activity of UGT73E1 homologous protein 1.
In FIG. 4, "Glc" denotes glucose.
FIG. 5 shows a chromatogram obtained for reference standards of
steviol and glycosides thereof.
FIG. 6 shows reaction pathways catalyzed by UGT73E1 homologous
protein 1. In FIG. 6, "UGT73E1HP1" denotes UGT73E1 homologous
protein 1.
The present invention will be described in more detail below. The
following embodiments are illustrated to describe the present
invention, and it is not intended to limit the present invention
only to these embodiments. The present invention can be implemented
in various modes, without departing from the spirit of the present
invention.
It should be noted that all publications cited herein, including
prior art documents, patent gazettes and other patent documents,
are incorporated herein by reference. Moreover, this specification
incorporates the contents disclosed in the specification and
drawings of Japanese Patent Application No. 2012-123349 (filed on
May 30, 2012), based on which the present application claims
priority.
The present invention will be described in more detail below. The
following embodiments are illustrated to describe the present
invention, and it is not intended to limit the present invention
only to these embodiments. The present invention can be implemented
in various modes, without departing from the spirit of the present
invention.
The inventors of the present invention have elucidated, ahead of
others, that stevia-derived UGT73E1 homologous protein 1 is an
enzyme protein responsible for sugar addition reaction in steviol
glycosides toward the 13-position hydroxy group and glucose bound
to the 13-position hydroxy group, as well as toward the 19-position
carboxyl group and glucose bound to the 19-position carboxyl
group.
The CDS sequence and deduced amino acid sequence of UGT73E1
homologous protein 1 are as shown in SEQ ID NOs: 1 and 2,
respectively. The above polynucleotide and enzyme can be obtained
by procedures as described later in the Example section, known
genetic engineering procedures, known synthesis procedures,
etc.
1. Steviol Glycosyltransferase
The present invention provides a protein of any one selected from
the group consisting of (a) to (c) shown below (hereinafter
referred to as "the protein of the present invention"):
(a) a protein which consists of the amino acid sequence shown in
SEQ ID NO: 2;
(b) a protein which consists of an amino acid sequence with
deletion, substitution, insertion and/or addition of 1 to 7 amino
acids in the amino acid sequence shown in SEQ ID NO: 2 and which
has the activity to add a sugar molecule(s) to --OR.sub.A at the
13-position and --COOR2 at the 19-position of a compound
represented by the following formula (I); and (c) a protein which
has an amino acid sequence sharing a sequence identity of 99% or
more with the amino acid sequence shown in SEQ ID NO: 2 and which
has the activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by the following formula (I)
##STR00009## (wherein R.sub.1 represents H, a glucose monomer or a
glucose dimer, and R.sub.2 represents H or a glucose monomer).
The above protein (b) or (c) is typically a mutant of the naturally
occurring polypeptide shown in SEQ ID NO: 2, although other
examples include those which may be artificially obtained by
site-directed mutagenesis as described in "Sambrook & Russell,
Molecular Cloning: A Laboratory Manual Vol. 3, Cold Spring Harbor
Laboratory Press 2001," "Ausubel, Current Protocols in Molecular
Biology, John Wiley & Sons 1987-1997," "Nuc. Acids. Res., 10,
6487 (1982)," "Proc. Natl. Acad. Sci. USA, 79, 6409 (1982)," "Gene,
34, 315 (1985)," "Nuc. Acids. Res., 13, 4431 (1985)," "Proc. Natl.
Acad. Sci. USA, 82, 488 (1985)," etc.
As used herein, the expression "protein which consists of an amino
acid sequence with deletion, substitution, insertion and/or
addition of 1 to 7 amino acids in the amino acid sequence shown in
SEQ ID NO: 2 and which has the activity to add a sugar molecule(s)
to --OR.sub.1 at the 13-position and --COOR.sub.2 at the
19-position of a compound represented by formula (I)" is intended
to include proteins which consist of an amino acid sequence with
deletion, substitution, insertion and/or addition of, e.g., 1 to 7
amino acid residues, 1 to 6 amino acid residues, 1 to 5 amino acid
residues, 1 to 4 amino acid residues, 1 to 3 amino acid residues, 1
to 2 amino acid residues, or a single amino acid residue in the
amino acid sequence shown in SEQ ID NO: 2 and which have the
activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by formula (I). In general, a smaller number is more
preferred for the above deletion, substitution, insertion and/or
addition of amino acid residues.
Moreover, examples of such proteins include those which have an
amino acid sequence sharing a sequence identity of 99% or more,
99.1% or more, 99.2% or more, 99.3% or more, 99.4% or more, 99.5%
or more, 99.6% or more, 99.7% or more, 99.8% or more, or 99.9% or
more with the amino acid sequence shown in SEQ ID NO: 2 and which
have the activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by formula (I). In general, a larger value is more
preferred for the above sequence identity.
In the context of the present invention, the expression "activity
to add a sugar molecule(s) to --OR.sub.1 at the 13-position and
--COOR.sub.2 at the 19-position of a compound represented by
formula (I)" is intended to mean the ability to cause sugar
addition to --OR.sub.1 at the 13-position and --COOR.sub.2 at the
19-position of a compound represented by the following formula
(I).
##STR00010##
In formula (I), R.sub.1 represents H, a glucose monomer (-Glc) or a
glucose dimer (-Glc-Glc), and R.sub.2 represents H or a glucose
monomer (-Glc). Preferably, R.sub.2 is H when R.sub.1 is a glucose
dimer. In the glucose dimer, glucoses are preferably linked to each
other via a .beta.2,1 glycosidic linkage. Moreover, sugar molecules
to be added by the action of the protein of the present invention
to --OR.sub.1 at the 13-position and --COOR.sub.2 at the
19-position of a compound represented by formula (I) are each
preferably added via a .beta.2,1 glycosidic linkage in both cases
where R.sub.1 is a glucose monomer or a glucose dimer and where
R.sub.2 is a glucose monomer.
A preferred compound of formula (I) is steviol, steviolmonoside,
steviolbioside, rubusoside or Compound Y.
There is no particular limitation on the sugar molecules to be
added by the action of the protein of the present invention to
--OR.sub.1 at the 13-position and --COOR.sub.2 at the 19-position
of a compound represented by formula (I), although they may be
sugar molecules composed of one or more pentoses, hexoses or any
combination thereof. Examples of pentoses and hexoses are as
described above. The above sugar molecule is preferably a hexose,
and more preferably a hexose selected from the group consisting of
glucose, mannose and galactose. The above sugar molecule is most
preferably glucose.
The activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by formula (I) can be verified as follows: after
incubation at a temperature of 20.degree. C. to 40.degree. C. for
10 minutes to 2 hours in a neutral buffer of pH 6.0 to 8.0 (e.g.,
sodium phosphate buffer or potassium phosphate buffer) which
contains a test protein in an amount of 1 to 500 ng (preferably 50
to 200 ng, most preferably 100 ng), a UDP-sugar (e.g., UDP-glucose)
at 1 to 1000 .mu.M (preferably 100 to 700 .mu.M, most preferably
500 .mu.M) and a substrate compound (i.e., a compound of formula
(I)) at 1 to 500 .mu.M (preferably 100 to 500 .mu.M, most
preferably 250 .mu.M), the above substrate compound is purified and
analyzed by known procedures such as LC-MS analysis (liquid
chromatography-mass spectrometry), etc.
If a compound having a sugar molecule(s) added to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by formula (I) is detected as a result of LC-MS
analysis, the above test protein can be regarded as having the
activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by formula (I).
The above sugar addition reaction is normally completed within
about 1 minute to about 12 hours.
Deletion, substitution, insertion and/or addition of one or several
amino acid residues in the amino acid sequence of the protein of
the present invention is intended to mean that deletion,
substitution, insertion and/or addition of one or several amino
acid residues occurs at any one or more positions in the same
sequence, and two or more of deletion, substitution, insertion and
addition may occur at the same time.
Examples of interchangeable amino acid residues are shown below.
Amino acid residues included in the same group are interchangeable
with each other. Group A: leucine, isoleucine, norleucine, valine,
norvaline, alanine, 2-aminobutanoic acid, methionine,
o-methylserine, t-butylglycine, t-butylalanine, cyclohexylalanine;
Group B: aspartic acid, glutamic acid, isoaspartic acid,
isoglutamic acid, 2-aminoadipic acid, 2-aminosuberic acid; Group C:
asparagine, glutamine; Group D: lysine, arginine, ornithine,
2,4-diaminobutanoic acid, 2,3-diaminopropionic acid; Group E:
proline, 3-hydroxyproline, 4-hydroxyproline; Group F: serine,
threonine, homoserine; Group G: phenylalanine, tyrosine.
Although the protein of the present invention may be obtained by
being expressed from a polynucleotide encoding it (see "the
polynucleotide of the present invention" described later) in
appropriate host cells, it may also be prepared by chemical
synthesis methods such as Fmoc method (fluorenylmethyloxycarbonyl
method) and tBoc method (t-butyloxycarbonyl method). Alternatively,
the protein of the present invention may also be chemically
synthesized with peptide synthesizers commercially available from
Advanced Automation Peptide Protein Technologies, Perkin Elmer,
Protein Technologies, PerSeptive, Applied Biosystems, SHIMADZU,
etc.
2. Method for Producing a Steviol Glycoside
The present invention enables the production of steviol glycosides
with ease and in large quantities by means of the activity of the
protein to add a sugar molecule(s) to --OR.sub.1 at the 13-position
and --COOR.sub.2 at the 19-position of a compound represented by
formula (I).
In another embodiment, the present invention therefore provides a
first method for producing a steviol glycoside, which comprises the
step of reacting the protein of the present invention, a UDP-sugar
and a compound represented by the following formula (I) to thereby
add a sugar molecule(s) to either or both of --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of the compound
represented by formula (I).
##STR00011##
R.sub.1 and R.sub.2 in formula (I) are as defined above. A
preferred compound of formula (I) is steviol, steviolmonoside,
steviolbioside, rubusoside or Compound Y.
As used herein, the term "UDP-sugar" refers to a uridine
diphosphate (UDP)-conjugated sugar. Preferred examples of the sugar
moiety of a UDP-sugar include sugars composed of one or more
pentoses, hexoses or any combination thereof. Examples of pentoses
and hexoses are as described above. The UDP-sugar is preferably a
UDP-hexose, and more preferably a hexose selected from the group
consisting of glucose, mannose and galactose. The above UDP-sugar
is most preferably UDP-glucose.
The first method for producing a steviol glycoside according to the
present invention comprises the step of reacting the protein of the
present invention, a UDP-sugar and a compound represented by
formula (I) to thereby add a sugar molecule(s) to either or both of
--OR.sub.1 at the 13-position and --COOR.sub.2 at the 19-position
of the compound represented by formula (I). The first method of the
present invention may further comprise the step of purifying the
steviol glycoside generated in the above step.
Examples of a steviol glycoside produced by the first method
include, but are not limited to, steviolmonoside, steviolbioside,
stevioside, rubusoside, Compound X, Compound Y, Compound Z or any
combination thereof.
The structure of Compound X is as shown below.
##STR00012##
The structure of Compound Y is as shown below.
##STR00013##
The structure of Compound Z is as shown below.
##STR00014##
The generated steviol glycosides can be purified by known
techniques such as extraction with an appropriate solvent (an
aqueous solvent such as water or an organic solvent such as
alcohol, ether or acetone), a gradient between an organic solvent
(e.g., ethyl acetate) and water, high performance liquid
chromatography (HPLC), gas chromatography, time-of-flight mass
spectrometry (TOF-MS), ultra (high) performance liquid
chromatography (UPLC), etc.
3. Non-Human Transformant Rich in Steviol Glycosides
Steviol glycosides may also be produced using the protein of the
present invention within cells such as those of bacteria (e.g., E.
coli or yeast), plants, insects, non-human mammals, etc. This is
because the protein of the present invention is an enzyme derived
from stevia or a mutant thereof and is therefore expected to have
high activity even in the intracellular environment. In this case,
a polynucleotide encoding the protein of the present invention (see
"the polynucleotide of the present invention" described later) may
be introduced into host cells derived from bacteria, plants,
insects, non-human mammals or the like to cause expression of the
protein of the present invention, followed by reacting the protein
of the present invention with UDP-sugars and compounds represented
by formula (I) present within the above cells to produce steviol
glycosides.
##STR00015##
Then, the present invention provides a non-human transformant
transformed with a polynucleotide of any one selected from the
group consisting of (a) to (d) shown below (hereinafter referred to
as "the polynucleotide of the present invention") (such a
transformant is hereinafter referred to as "the transformant of the
present invention"):
(a) a polynucleotide containing the nucleotide sequence shown in
SEQ ID NO: 1;
(b) a polynucleotide encoding a protein which consists of the amino
acid sequence shown in SEQ ID NO: 2;
(c) a polynucleotide encoding a protein which consists of an amino
acid sequence with deletion, substitution, insertion and/or
addition of 1 to 7 amino acids in the amino acid sequence shown in
SEQ ID NO: 2 and which has the activity to add a sugar molecule(s)
to --OR.sub.1 at the 13-position and --COOR.sub.2 at the
19-position of a compound represented by formula (I); and (d) a
polynucleotide encoding a protein which has an amino acid sequence
sharing a sequence identity of 99% or more with the amino acid
sequence shown in SEQ ID NO: 2 and which has the activity to add a
sugar molecule(s) to --OR.sub.1 at the 13-position and --COOR.sub.2
at the 19-position of a compound represented by formula (I).
The definition and detailed examples of formula (I) are as already
described above. Likewise, the definition and detailed examples of
sugar molecules to be added to --OR.sub.1 at the 13-position and
--COOR.sub.2 at the 19-position of a compound represented by
formula (I) are as described above.
As used herein, the term "polynucleotide" is intended to mean DNA
or RNA.
It should be noted that the sequence identity of amino acid
sequences or nucleotide sequences can be determined by using FASTA
(Science 227 (4693): 1435-1441, (1985)) or the algorithm of Karlin
and Altschul, BLAST (Basic Local Alignment Search Tool) (Proc.
Natl. Acad. Sci. USA 872264-2268, 1990; Proc Natl Acad Sci USA 90:
5873, 1993). Based on the algorithm of BLAST, programs called
blastn, blastx, blastp, tblastn and tblastx have been developed
(Altschul S F, et al: J Mol Biol 215: 403, 1990). If blastn is used
for nucleotide sequence analysis, parameters may be set to, for
example, score=100 and wordlength=12. Likewise, if blastp is used
for amino acid sequence analysis, parameters may be set to, for
example, score=50 and wordlength=3. If BLAST and Gapped BLAST
programs are used, default parameters in each program may be
used.
The above polynucleotides according to the present invention can be
obtained by known genetic engineering procedures or known synthesis
procedures.
The polynucleotide of the present invention is preferably
introduced into a host in a state of being inserted into an
appropriate expression vector.
An appropriate expression vector is generally configured to
comprise:
(i) a promoter transcribable in host cells;
(ii) the polynucleotide of the present invention ligated to the
promoter; and
(iii) an expression cassette comprising, as constituent elements,
signals that function in the host cells for transcription
termination and polyadenylation of an RNA molecule.
Such an expression vector may be prepared in any manner, for
example, by techniques using plasmids, phages or cosmids, etc.
The actual type of vector is not limited in any way, and any vector
expressible in host cells may be selected as appropriate. Namely, a
promoter sequence may be selected as appropriate for the type of
host cells in order to ensure expression of the polynucleotide of
the present invention, and this promoter and the polynucleotide of
the present invention may then be integrated into various plasmids
or the like for use as expression vectors.
The expression vector of the present invention contains an
expression control region(s) (e.g., a promoter, a terminator and/or
a replication origin), depending on the type of host into which the
expression vector is to be introduced. Promoters for use in
bacterial expression vectors may be commonly used promoters (e.g.,
trc promoter, tac promoter, lac promoter). Likewise, promoters for
use in yeast include, for example, glyceraldehyde triphosphate
dehydrogenase promoter, PH05 promoter and so on, while promoters
for use in filamentous fungi include, for example, amylase, trpC
and so on. In addition, examples of promoters used to express a
desired gene in plant cells include cauliflower mosaic virus 35S
RNA promoter, rd29A gene promoter, rbcS promoter, and mac-1
promoter that is configured to have the enhancer sequence of the
above cauliflower mosaic virus 35S RNA promoter at the 5'-side of
Agrobacterium-derived mannopine synthase promoter sequence.
Examples of promoters for use in animal cell hosts include viral
promoters (e.g., SV40 early promoter, SV40 late promoter) and so
on.
The expression vector preferably comprises at least one selection
marker. For this purpose, auxotrophic markers (ura5, niaD), drug
resistance markers (hygromycine, zeocin), geneticin resistance gene
(G418r), copper resistance gene (CUP 1) (Mann et al., Proc. Natl.
Acad. Sci. USA, vol. 81, p. 337, 1984), cerulenin resistance genes
(fas2m, PDR4) (Junji Inokoshi et al., Biochemistry, vol. 64, p.
660, 1992; Hussain et al., Gene, vol. 101, p. 149, 1991) and so on
are available for use.
Although the transformant of the present invention may be prepared
(produced) in any manner, an expression vector comprising the
polynucleotide of the present invention may be introduced into a
host to transform the host, by way of example.
The transformant of the present invention is expected to contain
steviol glycosides at high contents. Host cells used for
transformation may be of any type, and known various types of cells
can be used preferably. Examples of host cells include bacteria
such as E. coli, yeast (budding yeast Saccharomyces cerevisiae,
fission yeast Schizosaccharomyces pombe), plant cells, non-human
animal cells and so on.
Preferred host cells are those capable of producing a compound
represented by formula (I). In the context of the present
invention, host cells are not limited to those inherently capable
of producing a compound represented by formula (I), and may also
be, for example, those which have been recombinantly modified with
a known gene to be able to produce a compound represented by
formula (I).
Known examples of a gene encoding an enzyme contributing to the
synthesis of a compound represented by formula (I) include, but are
not limited to, EK13H, UGT74G1 and UGT76G1 (Non-patent Document
2).
In cases where host cells are not able to produce a compound
represented by formula (I), these host cells are transformed with
the gene of the present invention and the culture system of the
resulting transformant is supplemented with, as a substrate, a
compound of formula (I) or a plant extract containing this
compound, whereby steviol glycosides can be produced without the
need to introduce a gene encoding an enzyme contributing to the
synthesis of a compound represented by formula (I).
Culture media and conditions appropriate for the above host cells
are well known in the art. Moreover, the organism to be transformed
may be of any type, and examples include various types of
microorganisms or plants or non-human animals as listed above for
host cells.
For transformation of host cells, commonly used known techniques
can be used. For example, transformation may be accomplished by,
but is not limited to, electroporation (Mackenxie, D. A. et al.,
Appl. Environ. Microbiol., vol. 66, p. 4655-4661, 2000), particle
delivery method (described in JP 2005-287403 A), spheroplast method
(Proc. Natl. Acad. Sci. USA, vol. 75, p. 1929, 1978), lithium
acetate method (J. Bacteriology, vol. 153, p. 163, 1983), and other
methods as described in Methods in yeast genetics, 2000 Edition: A
Cold Spring Harbor Laboratory Course Manual.
In addition, as for standard molecular biological procedures,
reference may be made to "Sambrook & Russell, Molecular
Cloning: A Laboratory Manual Vol. 3, Cold Spring Harbor Laboratory
Press 2001," "Methods in Yeast Genetics, A laboratory manual (Cold
Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.),"
etc.
Upon culturing the thus obtained transformant, steviol glycosides
can be accumulated within the transformant. As described above, the
culture system of the transformant may be supplemented with, as a
substrate, a compound of formula (I) or a plant extract containing
this compound to thereby facilitate the production of steviol
glycosides. The accumulated steviol glycosides may be extracted and
purified to thereby obtain desired steviol glycosides.
Thus, the present invention provides a second method for producing
a steviol glycoside, which comprises using the transformant of the
present invention. Appropriate culture medium and conditions are
well known in the art. Moreover, how to extract and purify steviol
glycosides is as already described above.
Although steviol glycosides are not limited in any way, preferred
are those which may be selected from the group consisting of
steviolmonoside, steviolbioside, stevioside, rubusoside, Compound
X, Compound Y, Compound Z and combinations thereof.
In one embodiment of the present invention, the transformant may be
a plant transformant. The plant transformant according to this
embodiment may be obtained by introducing a recombinant vector
comprising the polynucleotide of the present invention into a plant
such that a polypeptide encoded by this polynucleotide can be
expressed.
In cases where a recombinant expression vector is used, any
recombinant expression vector may be used for transformation of a
whole plant as long as it is a vector allowing the polynucleotide
of the present invention to be expressed within the plant. Examples
of such a vector include those having a promoter which drives
constitutive expression of a desired polynucleotide within plant
cells or those having a promoter whose activation is induced by
external stimulation.
Examples of a promoter which drives constitutive expression of a
desired polynucleotide within plant cells include cauliflower
mosaic virus 35S RNA promoter, rd29A gene promoter, rbcS promoter,
mac-1 promoter, etc.
Examples of a promoter whose activation is induced by external
stimulation include mouse mammary tumor virus (MMTV) promoter,
tetracycline-responsive promoter, metallothionein promoter and heat
shock protein promoter, etc.
The plant to be transformed in the present invention is intended to
mean any of a whole plant, a plant organ (e.g., leaf, petal, stem,
root, seed), a plant tissue (e.g., epidermis, phloem, parenchyma,
xylem, vascular bundle, palisade tissue, spongy parenchyma) or a
plant cultured cell, or alternatively, various forms of plant cells
(e.g., suspension cultured cells), a protoplast, a leaf section, a
callus and so on. The plant used for transformation may be of any
type, belonging to either monocotyledons or dicotyledons.
For gene transfer into plants, transformation techniques known to
those skilled in the art may be used (e.g., Agrobacterium-mediated
method, gene gun method, PEG-mediated method, electroporation). For
example, Agrobacterium-mediated method and direct gene transfer
into plant cells are well known. In the case of using the
Agrobacterium-mediated method, the constructed plant expression
vector may be introduced into an appropriate Agrobacterium strain
(e.g., Agrobacterium tumefaciens) and this strain may then be
infected into a leaf section cultured under sterile conditions,
e.g., in accordance with the leaf disk method (Hirofumi Miyauchi,
Manuals for Plant Genetic Engineering (1990) pages 27-31, Kodansha
Scientific Ltd., Tokyo) to thereby obtain a transgenic plant.
Alternatively, it is possible to use the method of Nagel et al.
(Micribiol. Lett., 67: 325 (1990)). In this method, for example, an
expression vector is first introduced into Agrobacterium, and the
transformed Agrobacterium is then introduced into plant cells or
plant tissues as described in Plant Molecular Biology Manual
(Gelvin, S. B. et al., Academic Press Publishers). As used herein,
the term "plant tissue" also includes a callus obtainable by
culturing plant cells. In cases where the Agrobacterium-mediated
method is used for transformation, a binary vector (e.g., pBI121 or
pPZP202) may be used.
Likewise, techniques known for direct gene transfer into plant
cells or plant tissues are electroporation and particle gun method.
In the case of using a particle gun, a whole plant, a plant organ
or a plant tissue may be used directly, or sections may be prepared
therefrom before use, or protoplasts may be prepared and used. The
thus prepared samples may be treated using a gene transfer device
(e.g., PDS-1000 (BIO-RAD)). Although treatment conditions will vary
depending on the type of plant or sample, the treatment is
generally conducted at a pressure of about 450 to 2000 psi and at a
distance of about 4 to 12 cm.
The transformed cells or plant tissues are first selected by drug
resistance such as hygromycin resistance, and then regenerated into
whole plants in a standard manner. Regeneration from transformed
cells into whole plants may be accomplished by techniques known to
those skilled in the art as appropriate for the type of plant
cells.
In cases where cultured plant cells are used as a host,
transformation may be accomplished by introducing a recombinant
vector into the cultured cells with a gene gun or by
electroporation, etc. Calli, shoots, hairy roots and the like
obtained as a result of transformation may be used directly for
cell culture, tissue culture or organ culture, and may also be
regenerated into whole plants using conventionally known procedures
for plant tissue culture, e.g., by being administered with an
appropriate concentration of a plant hormone (e.g., auxin,
cytokinin, gibberellin, abscisic acid, ethylene, brassinolide).
Confirmation of whether or not the polynucleotide of the present
invention has been introduced into a plant may be accomplished by
PCR, Southern hybridization, Northern hybridization, etc. For
example, DNA is prepared from a transgenic plant and DNA specific
primers are designed for PCR. PCR may be performed under the same
conditions as used for preparation of the above plasmid. Then,
amplification products may be subjected to, e.g., agarose gel
electrophoresis, polyacrylamide gel electrophoresis or capillary
electrophoresis, followed by staining with ethidium bromide, SYBR
Green solution, etc. If the amplification products are detected as
a single band, it can be confirmed that the plant has been
transformed. Alternatively, primers which have been labeled with a
fluorescent dye or the like may be used in PCR to thereby detect
amplification products. Further, it is also possible to use
techniques in which amplification products are bound onto a solid
phase (e.g., a microplate) and confirmed by fluorescence or
enzymatic reaction, etc.
Once a transgenic whole plant whose genome carries the
polynucleotide of the present invention has been obtained, progeny
plants may be obtained by sexual or asexual reproduction of the
whole plant. Moreover, from such a whole plant or progeny plants
thereof or clones thereof, for example, seeds, fruits, cuttings,
tubers, root tubers, rootstocks, calli, protoplasts or the like may
be obtained and used to achieve mass production of the whole plant.
Thus, the present invention also encompasses a whole plant into
which the polynucleotide of the present invention has been
introduced in an expressible form, or progeny plants of the whole
plant which have the same properties as the whole plant, or tissues
derived from the whole plant and progeny plants thereof.
In addition, transformation techniques for various plants have
already been reported. Transgenic plants according to the present
invention include plants of the family Solanaceae (e.g., eggplant,
tomato, hot pepper, potato, tobacco, stramonium, Chinese lantern
plant, petunia, calibrachoa, nierembergia), plants of the family
Leguminosae (e.g., soybean, adzuki bean, peanut, kidney bean, broad
bean, Bird's foot trefoil), plants of the family Rosaceae (e.g.,
strawberry, Japanese apricot, cherry tree, rose, blueberry,
blackberry, bilberry, cassis, raspberry, Chinese blackberry),
plants of the family Caryophyllaceae (e.g., carnation, gypsophila),
plants of the family Asteraceae (e.g., chrysanthemum, gerbera,
sunflower, daisy, stevia), plants of the family Orchidaceae (e.g.,
orchid), plants of the family Primulaceae (e.g., cyclamen), plants
of the family Gentianaceae (e.g., showy prairie gentian, gentian),
plants of the family Iridaceae (e.g., freesia, iris, gladiolus),
plants of the family Scrophulariaceae (e.g., snapdragon, torenia),
stone crop (kalanchoe), plants of the family Liliaceae (e.g., lily,
tulip), plants of the family Convolvulaceae (e.g., morning glory,
ivy-leaved morning glory, moonflower, sweet potato, cypress vine,
evolvulus), plants of the family Hydrangeaceae (e.g., hydrangea,
deutzia), plants of the family Cucurbitaceae (e.g., bottle gourd),
plants of the family Geraniaceae (e.g., pelargonium, geranium),
plants of the family Oleaceae (e.g., weeping forsythia), plants of
the family Vitaceae (e.g., grape), plants of the family Theaceae
(e.g., camellia, tea plant), plants of the family Gramineae (e.g.,
rice, barley, wheat, oat, rye, maize, foxtail millet, Japanese
barnyard millet, kaoliang, sugar cane, bamboo, wild oat, finger
millet, sorghum, Manchurian wild rice, job's tears, pasture grass),
plants of the family Moraceae (e.g., mulberry, hop, paper mulberry,
rubber tree, cannabis), plants of the family Rubiaceae (e.g.,
coffee tree, gardenia), plants of the family Fagaceae (e.g., oak,
beech, Japanese emperor oak), plants of the family Pedaliaceae
(e.g., sesame), plants of the family Rutaceae (e.g., bitter orange,
Citrus junos, satsuma mandarin, Japanese pepper tree), plants of
the family Brassicaceae (e.g., red cabbage, flowering cabbage,
Japanese radish, white shepherd's purse, Chinese colza, cabbage,
broccoli, cauliflower), and plants of the family Lamiacea (e.g.,
salvia, perilla, lavender, skullcap). As examples particularly
preferred as plants to be transformed, those known to biosynthesize
various glycosides starting from steviol as an aglycon are desired
for use, and examples of such plants include stevia and Chinese
blackberry (Rubus suavissimus), etc.
When an appropriate substrate is present endogenously or added
externally, the whole plant transformed with the polynucleotide of
the present invention (hereinafter referred to as "the plant of the
present invention" or "the whole plant of the present invention")
is able to produce steviol glycosides in higher quantities than its
wild-type counterpart.
The plant of the present invention can be easily obtained as a
perfect whole plant by being grown from a seed, a cuttage, a bulb
or the like of the plant of the present invention.
Thus, the plant of the present invention encompasses a whole plant,
a plant organ (e.g., leaf, petal, stem, root, seed, bulb), a plant
tissue (e.g., epidermis, phloem, parenchyma, xylem, vascular
bundle, palisade tissue, spongy parenchyma) or a cultured plant
cell, or alternatively, various forms of plant cells (e.g.,
suspension cultured cells), a protoplast, a leaf section, a callus
and so on.
4. Extract of Transformant and Use Thereof
In another embodiment, the present invention also provides an
extract of the above transformant. When an appropriate substrate is
present endogenously or added externally, the transformant of the
present invention is rich in steviol glycosides as compared to its
wild-type counterpart; and hence an extract of the transformant is
considered to contain steviol glycosides at high
concentrations.
Such an extract of the transformant of the present invention can be
obtained as follows: the transformant is homogenized with, e.g.,
glass beads, a homogenizer or a sonicator and the resulting
homogenate is centrifuged to collect the supernatant. In addition,
a further extraction step may also be provided in accordance with
extraction procedures for steviol glycosides as mentioned
above.
The extract of the transformant of the present invention can be
provided for use in, e.g., production of foods, pharmaceutical
preparations and/or industrial raw materials according to standard
practice.
In another embodiment, the present invention also provides a food,
a pharmaceutical preparation and/or an industrial raw material
(e.g., raw materials for foods), each containing the extract of the
transformant of the present invention. Such a food, a
pharmaceutical preparation and/or an industrial raw material, each
containing the extract of the transformant of the present
invention, may be prepared in a standard manner. In this way, such
a food, a pharmaceutical preparation and/or an industrial raw
material, each containing the extract of the transformant of the
present invention, contains steviol glycosides generated by using
the transformant of the present invention.
The pharmaceutical preparation (composition) of the present
invention may be in any dosage form, such as solution, paste, gel,
solid, powder and other dosage forms. Moreover, the pharmaceutical
composition of the present invention may be used in external
preparations for skin (e.g., oil, lotion, cream, emulsion, gel,
shampoo, hair conditioner, nail enamel, foundation, lipstick, face
powder, facial pack, ointment, powder, dentifrice, aerosol,
cleansing foam), as well as bath preparations, hair growth
promoters, skin essences, sunscreening agents and so on.
The pharmaceutical composition of the present invention may further
comprise additional pharmaceutically active ingredients (e.g.,
anti-inflammatory ingredient) or auxiliary ingredients (e.g.,
lubricating ingredient, carrier ingredient), when required.
Examples of the food of the present invention include nutritional
supplementary foods, health foods, functional foods, children's
foods, geriatric foods and so on. The term "food" or "food product"
is used herein as a generic name for edible materials in the form
of solids, fluids, liquids or mixtures thereof.
The term "nutritional supplementary foods" refers to food products
enriched with specific nutritional ingredients. The term "health
foods" refers to food products that are healthful or good for
health, and encompasses nutritional supplementary foods, natural
foods and diet foods. The term "functional foods" refers to food
products for replenishing nutritional ingredients which assist body
control functions. Functional foods are synonymous with foods for
specified health use. The term "children's foods" refers to food
products given to children up to about 6 years old. The term
"geriatric foods" refers to food products treated to facilitate
digestion and absorption when compared to untreated foods.
In the food of the present invention, a calorie-less steviol
glycoside is used as a sweetener. For this reason, the food of the
present invention is low in calories and has the advantage of
contributing to health promotion or health maintenance.
These foods and food products may be in the form of agricultural
foods including bakery products, noodles, pastas, cooked rice,
sweets (e.g., cake, ice cream, ice lollies, doughnuts, pastries,
candies, chewing gums, gummies, tablets, as well as Japanese sweets
such as rice dumplings (dango) and sweet bean paste buns (manju)),
bean curd and processed products thereof; fermented foods including
Japanese rice wine (sake), medicinal liquor, sweet cooking sherry
(mirin), vinegar, soy sauce and miso (bean paste); livestock food
products including yogurt, ham, bacon and sausage; seafood products
including fish cake (kamaboko), deep-fried fish cake (ageten) and
puffy fish cake (hanpen); as well as fruit drinks, soft drinks,
sports drinks, alcoholic beverages, tea or flavor enhancers.
5. Screening Method for a Plant Rich in Steviol Glycosides
The present invention provides a screening method for a plant rich
in steviol glycosides. More specifically, the above method
comprises steps (1) to (3) shown below:
(1) the step of extracting mRNA from a test plant;
(2) the step of allowing hybridization between the above mRNA or
cDNA prepared from the above mRNA and a polynucleotide which is
hybridizable under high stringent conditions with a polynucleotide
consisting of a nucleotide sequence complementary to the
polynucleotide of the present invention; and (3) the step of
detecting the above hybridization.
The above step (1) may be accomplished by extracting mRNA from a
test plant. Although mRNA may be extracted from any site of the
test plant, preferred are petals. Once mRNA has been extracted,
cDNA may be prepared from the mRNA through reverse
transcription.
The above step (2) may be accomplished as follows: a polynucleotide
or oligonucleotide consisting of a nucleotide sequence
complementary to the polynucleotide of the present invention is
used as a probe or primer and allowed to hybridize with the mRNA
extracted above under high stringent conditions. As used herein,
the term "high stringent conditions" refers to, for example, but is
not limited to, the following conditions: (1) 5.times.SSC,
5.times.Denhardt's solution, 0.5% SDS, 50% formamide, 50.degree.
C.; (2) 0.2.times.SSC, 0.1% SDS, 60.degree. C.; (3) 0.2.times.SSC,
0.1% SDS, 62.degree. C.; or (4) 0.2.times.SSC, 0.1% SDS, 65.degree.
C. Under these conditions, it can be expected that DNA having a
higher sequence identity is efficiently obtained at a higher
temperature. However, the stringency of hybridization would be
affected by a plurality of factors, including temperature, probe
concentration, probe length, ionic strength, reaction time, salt
concentration and so on. Those skilled in the art would be able to
achieve the same stringency by selecting these factors as
appropriate.
Such a polynucleotide or oligonucleotide has a length of preferably
5 to 500 bp, more preferably 10 to 200 bp, and even more preferably
10 to 100 bp. The polynucleotide or oligonucleotide may be readily
synthesized with various automatic synthesizers (e.g., AKTA
oligopilot plus 10/100 (GE Healthcare)), or alternatively, its
synthesis may be entrusted to a third party (e.g., Promega or
Takara), etc.
When the polynucleotide consisting of a nucleotide sequence
complementary to the polynucleotide of the present invention is
used as a probe in the step (2), the step (3) may be accomplished
by commonly used techniques for detection of hybridization, such as
Southern blotting, Northern blotting (Sambrook, Fritsch and
Maniatis, "Molecular Cloning: A Laboratory Manual" 2nd Edition
(1989), Cold Spring Harbor Laboratory Press), microarrays
(Affymetrix; see U.S. Pat. Nos. 6,045,996, 5,925,525 and
5,858,659), TaqMan PCR (Sambrook, Fritsch and Maniatis, "Molecular
Cloning: A Laboratory Manual" 2nd Edition (1989), Cold Spring
Harbor Laboratory Press), or fluorescent in situ hybridization
(FISH) (Sieben V. J. et al., (2007-06). IET Nanobiotechnology 1
(3): 27-35). On the other hand, when the polynucleotide consisting
of a nucleotide sequence complementary to the polynucleotide of the
present invention is used as a primer in the step (2), the step (3)
may be accomplished by PCR amplification and the subsequent
analysis of the resulting amplification products by electrophoresis
or sequencing (Sambrook, Fritsch and Maniatis, "Molecular Cloning:
A Laboratory Manual" 2nd Edition (1989), Cold Spring Harbor
Laboratory Press), etc., to detect hybridization.
A whole plant in which hybridization was more often detected can be
regarded as expressing higher levels of a protein having the
activity to add a sugar molecule(s) to --OR.sub.1 at the
13-position and --COOR.sub.2 at the 19-position of a compound
represented by the following formula (I) than other whole plants,
and hence such a whole plant is predicted to be rich in steviol
glycosides.
##STR00016##
EXAMPLES
The present invention will now be described in more detail by way
of the following examples, which are not intended to limit the
scope of the present invention.
[Example 1] Isolation of Candidate Gene for Steviolbioside
Glycosyltransferase
To obtain a gene highly homologous to UGT73E1 (AY345979) which has
been reported to have no glycosylation activity on steviol
glycosides in previous studies (Non-patent Document 2), cDNA
prepared from stevia leaves was used as a template in PCR with the
following primer set (SEQ ID NOs: 3 and 4).
The stevia leaf cDNA was obtained as follows: total RNA was
extracted from stevia leaves with an RNeasy Plant Mini kit
(QIAGEN), and 0.5 .mu.g of the total RNA was then subjected to
reverse transcription (RT) reaction with random oligo-dT
primers.
TABLE-US-00001 CACC-NdeI-SrUGT73E1-Fw: (SEQ ID NO: 3)
5'-CACCCATATGTCGCCAAAAATGGTGGCACCA-3' BamHI-SrUGT73E1-Rv: (SEQ ID
NO: 4) 5'-GGATCCCTAATGTGGTGCTCTAACTGTTTCAGTCACAT-3'
A PCR reaction solution (50 .mu.l) was prepared to consist of
stevia leaf-derived cDNA (1 .mu.l), 1.times.ExTaq buffer
(TaKaRaBio), 0.2 mM dNTPs, primers (0.4 pmol/.mu.l each) and ExTaq
polymerase (2.5 U). The PCR reaction was accomplished by incubation
at 94.degree. C. for 3 minutes and the subsequent amplification in
which reactions at 94.degree. C. for 1 minute, at 50.degree. C. for
1 minute and at 72.degree. C. for 2 minutes were repeated for 30
cycles in total. The PCR products were electrophoresed on a 0.8%
agarose gel and stained with ethidium bromide, thereby resulting in
an amplified band at a size of approximately 1.5 kb predicted from
each template DNA.
This PCR product was subcloned into pENTR-TOPO Directional vector
(Invitrogen) in accordance with the method recommend by the
manufacturer. The clone was sequenced by primer walking with
synthetic oligonucleotide primers using a DNA Sequencer model 3100
(Applied Biosystems).
As a result of the sequence analysis of the cloned cDNA (designated
as "UGT73E1 homologous protein 1"), it showed a sequence identity
of 98% at the DNA level (a difference of 16 bases) and a sequence
identity of 98% at the amino acid level (a difference of 8 amino
acids) (CDS sequence: SEQ ID NO: 1, amino acid sequence: SEQ ID NO:
2) relative to the reported UGT73E1.
[Example 2] Construction of Expression Vector
An approximately 1.5 kb ORF fragment of UGT73E1 homologous protein
1 was excised by means of the NdeI and BamHI restriction enzyme
sites (the underlined parts in SEQ ID NOs: 3 and 4) added to the
primers and then was ligated to the NdeI and BamHI sites of an E.
coli expression vector, pET15b (Novagen), to thereby obtain an E.
coli expression vector for this enzyme gene. This vector was
designed to carry the open reading frame of the UGT73E1 homologous
protein 1 gene in frame with a His tag located upstream of the NdeI
site of this vector and to express a chimeric protein fused between
UGT73E1 homologous protein 1 and the His tag.
[Example 3] Expression and Purification of Recombinant Protein
To clarify biochemical functions of this enzyme, this enzyme was
allowed to be expressed in E. coli cells. The UGT73E1 homologous
protein 1 E. coli expression plasmid obtained above was used to
transform E. coli strain BL21(DE3) in a standard manner. The
resulting transformant was cultured overnight at 37.degree. C.
under shaking conditions in 4 ml of a 50 .mu.g/ml
ampicillin-containing LB medium (10 g/1 typtone pepton, 5 g/1 yeast
extract, 1 g/1 NaCl). After reaching the resting phase, the
cultured solution (4 ml) was inoculated into a medium of the same
composition (80 ml) and cultured at 37.degree. C. under shaking
conditions. At the time point where the cell turbidity (OD600)
reached about 0.5, IPTG was added at a final concentration of 0.5
mM, followed by culturing at 18.degree. C. for 20 hours under
shaking conditions.
The following manipulations were all performed at 4.degree. C. The
cultured transformant was collected by centrifugation
(5,000.times.g, 10 min) and then added to and suspended in Buffer S
[20 mM HEPES buffer (pH 7.5), 20 mM imidazole, 14 mM
.beta.-mercaptoethanol] at 1 ml/g cell. Subsequently, the
suspension was homogenized by ultrasonication (15 sec, repeated 8
times) and then centrifuged (15,000.times.g, 15 min). The resulting
supernatant was collected as a crude enzyme solution. The crude
enzyme solution was loaded onto a His SpinTrap column (GE
Healthcare) which had been equilibrated with Buffer S, followed by
centrifugation (70.times.g, 30 sec). After washing with the buffer,
proteins bound to the column were eluted stepwise with 5 ml each of
Buffer S containing 100 mM and 500 mM imidazole. Each elution
fraction was subjected to buffer replacement with 20 mM HEPES
buffer (pH 7.5), 14 mM .beta.-mercaptoethanol through a Microcon
YM-30 unit (Amicon) (magnification of dialysis: .times.1000).
As a result of SDS-PAGE separation and the subsequent CBB staining,
in the fraction eluted with 200 mM imidazole, a protein was
confirmed at approximately 50 kDa (indicated with an asterisk in
FIG. 3), which is the putative molecular weight for the
HisTag-fused UGT73E1 homologous protein 1 chimeric protein. This
fraction was used for enzyme analysis. It should be noted that in
FIG. 3, panel A shows a CBB-stained image obtained for the pellet
fraction, while panel B shows a CBB-stained image obtained for the
fraction eluted with the imidazole solution.
[Example 4] Measurement of Enzyme Activity of UGT73E1 Homologous
Protein 1
Standard enzyme reaction conditions are as follows. A reaction
solution (2 mM UDP-glucose, 0.1 mM sugar acceptor substrate
(steviol), 100 mM potassium phosphate buffer (pH 7.0), 25 .mu.l
purified UGT73E1 homologous protein 1 enzyme solution) was prepared
in a volume of 50 .mu.l with distilled water and reacted at
30.degree. C. for 1 hour. The enzyme reaction solution (5 .mu.l)
was analyzed by LC-MS under the following conditions.
LC conditions
Column: Waters Sunfire C18 3.5 um (2.0 mm I.D..times.20 mm)
Mobile phase: A: MilliQ Water (+0.05% formic acid), B: MeCN
Gradient: linear concentration gradient of B from 15% to 55% over
20 minutes
Flow rate: 0.2 ml per minute
Column oven: 40.degree. C.
MS conditions
ESI (negative mode)
Selected ion monitoring: m/z 317, 479, 641, 687, 803 and 849
As a result of the reaction between UGT73E1 homologous protein 1
and steviol, four types of products were newly found in the
reaction solution between UGT73E1 homologous protein 1 and steviol
(peak A) (FIG. 4: panel 1). Among them, peak E and peak B were
identified to be rubusoside and steviolmonoside, respectively,
based on comparison with the retention times of their reference
standards (FIG. 5).
On the other hand, with respect to the remaining two peaks, based
on their MS chromatograms, Compound Y was identified to be a
monoglucoside and Compound X was identified to be a diglucoside.
The retention time of Compound Y was not in agreement with that of
the reference standard steviolmonoside, thus suggesting that
Compound Y was a monoglucoside in which the carboxyl group at the
19-position of steviol was monoglycosylated (FIG. 6). Likewise, the
retention time of Compound X was not in agreement with that of
steviolbioside or rubusoside, each being a diglucoside of steviol,
thus strongly suggesting that the carboxyl group at the 19-position
was glucosylated (FIG. 6). When UGT73E1 homologous protein 1 and
UGT85C2 were simultaneously reacted with steviol (peak A), the
peaks of Compound Y and Compound X were both reduced significantly
(FIG. 4: panel 2). This would be because these two enzymes are in a
competitive relationship where steviol is used in common as a
substrate, and hence steviol (peak A) was rapidly converted into
steviolmonoside (peak B) by the action of UGT85C2.
Furthermore, upon reaction between UGT73E1 homologous protein 1 and
rubusoside (peak E), Compound Z which appears to be a triglucoside
of steviol was newly generated (FIG. 4: panel 3). The retention
time of Compound Z was not in agreement with those of stevioside
and rebaudioside B (peaks F and D), each being a triglucoside of
steviol, thus suggesting that the glucose at the 19-position of
rubusoside was further glucosylated (FIG. 6).
Upon reaction between UGT73E1 homologous protein 1 and
steviolmonoside (peak B), two peaks (peak E and peak F) were newly
obtained (FIG. 4: panel 4). Based on their retention times, peak E
was identified to be rubusoside and peak F was identified to be
stevioside. Further, upon reaction between UGT73E1 homologous
protein 1 and steviolbioside (peak C), a product which appears to
be stevioside (peak F) was also detected (FIG. 4: panel 5).
In light of these results, UGT73E1 homologous protein 1 causes
glucosylation at the 13-position hydroxy group of steviol to
generate steviolmonoside, and causes further glucosylation at the
13-position glucose of steviolmonoside to generate steviolbioside,
and causes further glucosylation at the 19-position carboxyl group
of steviolbioside to generate stevioside. As shown above, UGT73E1
homologous protein 1 was found to have glucosylation activity on
the 19-position of steviolmonoside to generate rubusoside. However,
no significant stevioside peak can be found in the reaction
solution between rubusoside and UGT73E1 homologous protein 1, thus
suggesting that stevioside, a reaction product of UGT73E1
homologous protein 1, is generated via steviolbioside (FIG. 6).
INDUSTRIAL APPLICABILITY
In view of the foregoing, UGT73E1 homologous protein 1 was found to
be a multifunctional glucosylation enzyme capable of reacting with
steviol and various glucosides thereof (FIG. 6). This enzyme was
found to be specific for different positions because it
glucosylated steviol at the 13-position hydroxy group, further at
the 19-position carboxyl group and further at the 19-position
glucose. With the use of this enzyme, known steviol glycosides can
be produced by a novel method. Moreover, structurally novel steviol
glycosides can also be produced.
SEQUENCE LISTING FREE TEXT
SEQ ID NO: 3: synthetic DNA
SEQ ID NO: 4: synthetic DNA
Sequence Listing
SEQUENCE LISTINGS
1
411488DNAStevia rebaudianaCDS(1)..(1485) 1atg tcg cca aaa atg gtg
gca cca cca acc aac ctt cat ttt gtt ttg 48Met Ser Pro Lys Met Val
Ala Pro Pro Thr Asn Leu His Phe Val Leu 1 5 10 15 ttt cct ctt atg
gct caa ggc cat ctg gta ccc atg gtc gac atc gct 96Phe Pro Leu Met
Ala Gln Gly His Leu Val Pro Met Val Asp Ile Ala 20 25 30 cga atc
tta gcc caa cgt ggt gca acg gtc acc ata atc acc aca ccc 144Arg Ile
Leu Ala Gln Arg Gly Ala Thr Val Thr Ile Ile Thr Thr Pro 35 40 45
tac gat gcc aac cgg gtc aga ccg gtt atc tcc cga gcc atc gcg acc
192Tyr Asp Ala Asn Arg Val Arg Pro Val Ile Ser Arg Ala Ile Ala Thr
50 55 60 aat ctc aag atc cag cta ctc gaa ctc caa ctg cgg tca acc
gaa gcc 240Asn Leu Lys Ile Gln Leu Leu Glu Leu Gln Leu Arg Ser Thr
Glu Ala 65 70 75 80 ggt tta ccc gaa ggg tgc gaa agc ttc gac caa ctt
ccg tca ttc gag 288Gly Leu Pro Glu Gly Cys Glu Ser Phe Asp Gln Leu
Pro Ser Phe Glu 85 90 95 tac tgg aaa aat att tca acc gct atc cat
ttg tta caa caa ccc gct 336Tyr Trp Lys Asn Ile Ser Thr Ala Ile His
Leu Leu Gln Gln Pro Ala 100 105 110 gaa gat ttg ctc cga gaa ctt tca
cca cca ccc gat tgc atc ata tcg 384Glu Asp Leu Leu Arg Glu Leu Ser
Pro Pro Pro Asp Cys Ile Ile Ser 115 120 125 gac ttt tgg ttc ccg tgg
acc acc gat gtg gct cga cgg tta aac atc 432Asp Phe Trp Phe Pro Trp
Thr Thr Asp Val Ala Arg Arg Leu Asn Ile 130 135 140 ccc cgg ctc gtg
ttc aac gga aag ggc tgc ttt tat ccc ttg tgc atg 480Pro Arg Leu Val
Phe Asn Gly Lys Gly Cys Phe Tyr Pro Leu Cys Met 145 150 155 160 cat
gtt gcg atc act tcc aac att ttg gga gag aat gaa ccg gtc agt 528His
Val Ala Ile Thr Ser Asn Ile Leu Gly Glu Asn Glu Pro Val Ser 165 170
175 agt aat acc gag cgc gtt gtg ctg ccc ggt tta cct gac cgg atc gaa
576Ser Asn Thr Glu Arg Val Val Leu Pro Gly Leu Pro Asp Arg Ile Glu
180 185 190 gtc act aaa ctt cag atc ctc ggt tcg tcg aga cca gcc aac
gta gac 624Val Thr Lys Leu Gln Ile Leu Gly Ser Ser Arg Pro Ala Asn
Val Asp 195 200 205 gaa atg ggc tcg tgg ctt cga gcc gta gaa gcc gag
aaa gct tca ttc 672Glu Met Gly Ser Trp Leu Arg Ala Val Glu Ala Glu
Lys Ala Ser Phe 210 215 220 ggg ata gtg gtt aat act ttc gaa gag ctt
gaa ccg gag tac gtt gaa 720Gly Ile Val Val Asn Thr Phe Glu Glu Leu
Glu Pro Glu Tyr Val Glu 225 230 235 240 gaa tac aaa acg gtt aaa gat
aag aag atg tgg tgt atc ggc ccg gtt 768Glu Tyr Lys Thr Val Lys Asp
Lys Lys Met Trp Cys Ile Gly Pro Val 245 250 255 tcg tta tgc aac aaa
acc ggg ccg gat tta gcc gag cga gga aac aag 816Ser Leu Cys Asn Lys
Thr Gly Pro Asp Leu Ala Glu Arg Gly Asn Lys 260 265 270 gct gca ata
acc gaa cac aac tgc tta aaa tgg ctc gat gag aga aaa 864Ala Ala Ile
Thr Glu His Asn Cys Leu Lys Trp Leu Asp Glu Arg Lys 275 280 285 ctg
ggg tcc gtg tta tac gtt tgt tta ggt agc ctt gca cgc att tct 912Leu
Gly Ser Val Leu Tyr Val Cys Leu Gly Ser Leu Ala Arg Ile Ser 290 295
300 acc gca caa gca atc gag ctc ggg tta gga ctc gag tcc ata aac cga
960Thr Ala Gln Ala Ile Glu Leu Gly Leu Gly Leu Glu Ser Ile Asn Arg
305 310 315 320 ccc ttt ata tgg tgc gta aga aac gaa acc gat gag ctc
aaa aca tgg 1008Pro Phe Ile Trp Cys Val Arg Asn Glu Thr Asp Glu Leu
Lys Thr Trp 325 330 335 ttt ttg gat ggg ttt gaa gaa agg gtt aga gat
cgc ggg ttg atc gtt 1056Phe Leu Asp Gly Phe Glu Glu Arg Val Arg Asp
Arg Gly Leu Ile Val 340 345 350 cat ggt tgg gcg cca cag gtt ttg ata
ctg tcg cac cca acc att ggc 1104His Gly Trp Ala Pro Gln Val Leu Ile
Leu Ser His Pro Thr Ile Gly 355 360 365 ggt ttc ttg acc cat tgc ggt
tgg aac tcg act att gaa tcg att acc 1152Gly Phe Leu Thr His Cys Gly
Trp Asn Ser Thr Ile Glu Ser Ile Thr 370 375 380 gcg ggt gtt cca atg
atc acg tgg ccg ttt ttt gcg gac cag ttt ttg 1200Ala Gly Val Pro Met
Ile Thr Trp Pro Phe Phe Ala Asp Gln Phe Leu 385 390 395 400 aat gaa
gct ttt ata gtt gaa gtt ttg aag att gga gtt agg att ggt 1248Asn Glu
Ala Phe Ile Val Glu Val Leu Lys Ile Gly Val Arg Ile Gly 405 410 415
gtt gag aga gct tgt tcg ttt ggg gaa gaa gat aag gtt gga gtg ttg
1296Val Glu Arg Ala Cys Ser Phe Gly Glu Glu Asp Lys Val Gly Val Leu
420 425 430 gtg aag aag gag gat gtg aaa aag gct gtt gaa tgc ttg atg
gat gaa 1344Val Lys Lys Glu Asp Val Lys Lys Ala Val Glu Cys Leu Met
Asp Glu 435 440 445 gat gaa gat ggt gat cag aga aga aag agg gtg att
gag ctt gca aaa 1392Asp Glu Asp Gly Asp Gln Arg Arg Lys Arg Val Ile
Glu Leu Ala Lys 450 455 460 atg gcg aag att gca atg gcg gaa ggt gga
tct tct tat gaa aat gta 1440Met Ala Lys Ile Ala Met Ala Glu Gly Gly
Ser Ser Tyr Glu Asn Val 465 470 475 480 tcg tcg ttg att cga gat gtg
act gaa aca gtt aga gca cca cat tag 1488Ser Ser Leu Ile Arg Asp Val
Thr Glu Thr Val Arg Ala Pro His 485 490 495 2495PRTStevia
rebaudiana 2Met Ser Pro Lys Met Val Ala Pro Pro Thr Asn Leu His Phe
Val Leu 1 5 10 15 Phe Pro Leu Met Ala Gln Gly His Leu Val Pro Met
Val Asp Ile Ala 20 25 30 Arg Ile Leu Ala Gln Arg Gly Ala Thr Val
Thr Ile Ile Thr Thr Pro 35 40 45 Tyr Asp Ala Asn Arg Val Arg Pro
Val Ile Ser Arg Ala Ile Ala Thr 50 55 60 Asn Leu Lys Ile Gln Leu
Leu Glu Leu Gln Leu Arg Ser Thr Glu Ala 65 70 75 80 Gly Leu Pro Glu
Gly Cys Glu Ser Phe Asp Gln Leu Pro Ser Phe Glu 85 90 95 Tyr Trp
Lys Asn Ile Ser Thr Ala Ile His Leu Leu Gln Gln Pro Ala 100 105 110
Glu Asp Leu Leu Arg Glu Leu Ser Pro Pro Pro Asp Cys Ile Ile Ser 115
120 125 Asp Phe Trp Phe Pro Trp Thr Thr Asp Val Ala Arg Arg Leu Asn
Ile 130 135 140 Pro Arg Leu Val Phe Asn Gly Lys Gly Cys Phe Tyr Pro
Leu Cys Met 145 150 155 160 His Val Ala Ile Thr Ser Asn Ile Leu Gly
Glu Asn Glu Pro Val Ser 165 170 175 Ser Asn Thr Glu Arg Val Val Leu
Pro Gly Leu Pro Asp Arg Ile Glu 180 185 190 Val Thr Lys Leu Gln Ile
Leu Gly Ser Ser Arg Pro Ala Asn Val Asp 195 200 205 Glu Met Gly Ser
Trp Leu Arg Ala Val Glu Ala Glu Lys Ala Ser Phe 210 215 220 Gly Ile
Val Val Asn Thr Phe Glu Glu Leu Glu Pro Glu Tyr Val Glu 225 230 235
240 Glu Tyr Lys Thr Val Lys Asp Lys Lys Met Trp Cys Ile Gly Pro Val
245 250 255 Ser Leu Cys Asn Lys Thr Gly Pro Asp Leu Ala Glu Arg Gly
Asn Lys 260 265 270 Ala Ala Ile Thr Glu His Asn Cys Leu Lys Trp Leu
Asp Glu Arg Lys 275 280 285 Leu Gly Ser Val Leu Tyr Val Cys Leu Gly
Ser Leu Ala Arg Ile Ser 290 295 300 Thr Ala Gln Ala Ile Glu Leu Gly
Leu Gly Leu Glu Ser Ile Asn Arg 305 310 315 320 Pro Phe Ile Trp Cys
Val Arg Asn Glu Thr Asp Glu Leu Lys Thr Trp 325 330 335 Phe Leu Asp
Gly Phe Glu Glu Arg Val Arg Asp Arg Gly Leu Ile Val 340 345 350 His
Gly Trp Ala Pro Gln Val Leu Ile Leu Ser His Pro Thr Ile Gly 355 360
365 Gly Phe Leu Thr His Cys Gly Trp Asn Ser Thr Ile Glu Ser Ile Thr
370 375 380 Ala Gly Val Pro Met Ile Thr Trp Pro Phe Phe Ala Asp Gln
Phe Leu 385 390 395 400 Asn Glu Ala Phe Ile Val Glu Val Leu Lys Ile
Gly Val Arg Ile Gly 405 410 415 Val Glu Arg Ala Cys Ser Phe Gly Glu
Glu Asp Lys Val Gly Val Leu 420 425 430 Val Lys Lys Glu Asp Val Lys
Lys Ala Val Glu Cys Leu Met Asp Glu 435 440 445 Asp Glu Asp Gly Asp
Gln Arg Arg Lys Arg Val Ile Glu Leu Ala Lys 450 455 460 Met Ala Lys
Ile Ala Met Ala Glu Gly Gly Ser Ser Tyr Glu Asn Val 465 470 475 480
Ser Ser Leu Ile Arg Asp Val Thr Glu Thr Val Arg Ala Pro His 485 490
495 331DNAArtificial SequenceDescription of Artificial Sequence
Synthetic primer 3cacccatatg tcgccaaaaa tggtggcacc a
31438DNAArtificial SequenceDescription of Artificial Sequence
Synthetic primer 4ggatccctaa tgtggtgctc taactgtttc agtcacat 38
* * * * *